This invention relates to a method of purifying a mixture of chlorine with other gases in apparatus that is suitable for contacting the mixture with carbon tetrachloride in order to remove one of the gases from the mixture. Specifically, it relates to contacting the mixture of gases in that apparatus with either chloroform or ethylene dichloride.
In the manufacture and use of chlorine, mixtures of chlorine with other relatively harmless gases, such as oxygen and carbon dioxide, are often produced. If the concentration of chlorine in these gases is relatively high the bulk of the chlorine can be removed by liquification of the chlorine. Removal of the remaining small concentrations of chlorine from the gas mixture was often accomplished by mixing the gases with carbon tetrachloride. The carbon tetrachloride would absorb the chlorine so that the remaining gases could be released to the atmosphere. Heating then released the chlorine from the carbon tetrachloride. However, this process resulted in small amounts of carbon tetrachloride being released to the atmosphere.
Under the Montreal Protocol, which went into effect in July of 1993, the use of carbon tetrachloride has been discouraged by heavy taxes and its use will be banned altogether in the future. In order to comply with these regulations it was necessary to find another suitable solvent that could absorb the chlorine. While there are a large number of solvents that are good chlorine absorbers, many of these solvents are not suitable for this type of application because they are toxic, flammable, too high boiling, too low boiling, corrosive, or react with the chlorine. Many of the solvents would require expensive modifications of the gas purification apparatus, such as increasing the heat duty, using larger equipment, or using a source of heat other than steam.
Carbon tetrachloride was also used to remove contaminants, such as nitrogen trichloride and high boiling compounds, from chlorine. The carbon tetrachloride was mixed with gaseous chlorine and the contaminants were absorbed into the carbon tetrachloride. Heating the mixture of carbon tetrachloride and contaminants resulted in the decomposition of the nitrogen trichloride. This application for carbon tetrachloride is also discouraged under the Montreal Protocol.